“Carbonation” refers to dissolving carbon dioxide (CO2) in an aqueous solution. Carbonated beverages are potable liquids into which carbon dioxide (CO2) has been dissolved. One group of carbonated beverages includes carbonated soft drinks (CSDs). Unlike beer, sparkling wine and other beverages that rely on fermentation to achieve carbonation, CSDs are typically non-alcoholic and carbonated by a mechanical mixing process. That mixing process is usually performed in a large reactor and involves high pressure flows of gaseous CO2, low beverage temperatures and large surface area contact between the gaseous CO2 and liquid beverage. The reactors often include spargers, diffusers and/or other equipment used to increase the surface area of liquid/CO2 contact. Carbonation by such mechanical mixing processes is normally performed under super-atmospheric pressure so as to achieve a CO2 concentration in the beverage that exceeds CO2 under atmospheric conditions.
Conventional carbonation of CSDs may require expensive and specialized equipment, particularly when performed on a large scale. Once carbonated, a CSD must usually be maintained at an elevated pressure prior to placing the CSD into a bottle or other consumer product container. When a consumer product container is filled with a CSD, the filling must usually be performed using specialized filling heads that carefully control pressure.
Various attempts have been made to perform carbonation after placing liquid into a consumer product container (i.e., “post-fill”). For example, U.S. Pat. No. 3,607,303 describes placing a syrup-water mixture into a container such as a can. The '303 patent further describes placing a slug of solid CO2 into the container prior to sealing. French patent 2,799,137 and international patent application publication WO 94/15489 similarly describe adding solid carbon dioxide to a liquid in a container prior to sealing of that container.
Post-fill carbonation by addition of solid CO2 (dry ice) poses problems, however. Dry ice vigorously sublimes when it is placed into a liquid having a significantly higher temperature than the dry ice. This sublimation generates gaseous CO2 at a very rapid rate. Because of limited surface area between that gaseous CO2 and the beverage within a sealed container, the rate at which CO2 dissolves into the beverage can be relatively slow. As a result, pressure within the sealed container may rise significantly as the sublimating dry ice gives off gaseous CO2 faster than the gaseous CO2 can be absorbed by dissolution into the beverage. This pressure can deform the container.
Although the prior art has recognized this problem to at least some degree, proposed solutions are less than satisfactory. For example, the aforementioned U.S. Pat. No. 3,607,303 indicates that the beverage should be placed into the container while the beverage is still near its freezing point. This purportedly results in a slug of solid CO2 being encapsulated by an ice film that acts to control the rate of sublimation. As another example, publication WO 94/15489 describes “partially” carbonating the beverage using gaseous CO2 prior to adding solid CO2.
There remains a need for improved methods and systems that permit post-fill carbonation of CSDs while limiting overpressures in a sealed CSD container.